title: Rechallenge prior sildenafil nonresponders.
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D007172:Erectile Dysfunction / Q000188:drug therapy*; D005240:Feasibility Studies; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D010045:Outpatients; D010353:Patient Education as Topic; D010879:Piperazines / Q000008:administration & dosage*; D011687:Purines; D016879:Salvage Therapy; D000068677:Sildenafil Citrate; D013450:Sulfones; D011795:Surveys and Questionnaires; D017211:Treatment Failure; D014665:Vasodilator Agents / Q000008:administration & dosage*
chemical_list: D010879:Piperazines; D011687:Purines; D013450:Sulfones; D014665:Vasodilator Agents; D000068677:Sildenafil Citrate